Proefschrift_vd

58 | Chapter 3

subgroups and do not reach significant levels. The resistances in transversal direction (r Trans ) are more than

a factor 100 higher than the corresponding r Long values (Fig. 7B). Therefore, a longitudinal conductivity

path along the array will dominate in all groups. As found for longitudinal resistances, the transversal

resistances along the array do not show significant differences between the groups. An important factor, as

indicated by the EFIM measurements, is the basal resistance (r Basal ) (Fig. 7C), which is at least 5 times

the r Long value in all groups. This is the resistance from the basal contact of the cochlea to the reference

electrode contact. This r Basal reveals differences between the subgroups. The basal resistance of the NPs-

subgroup is significantly lower than the r Basal of both the P-group and the NPd-group. In contrast to the

basal resistances, the tissue resistance, the global impedance between a given electrode and ground, does

not show significant differences between the Pand NP-groups (Fig. 7D). Moreover, the NPs and NPd show

comparable values (not plotted in Fig. 7D). However, the r Tissue of the NP-patients measured 1 or 2 mos

after implantation were lower at the basal side of the cochlea, differing significantly with the data obtained

after 1 yr (Fig. 7D). Also, the r Long and r Trans of the NP-group showed this basal increase.

Fig. 6.

T-levels of the positioner-group (P) and the nonpositioner-group (NP), shown per electrode contact (A) and per depth range (B).

The NP-group is split into the group of the first 9 shallowly inserted patients (NPs) and the last 11 deeper implanted patients (NPd).

Significant differences in basal increases in T-levels between the P-group and the NPs-group are marked (*

< 0.05; **

< 0.01). C and D

show the dynamic range of each group per electrode contact (C) and per insertion range (D). The number of patients in the subgroups is

shown for electrode pairs and for the depth ranges in Table 3.

sured with monosyllabic words (

0.64,

0.01,

0.55,

0.05, for the P and NP groups,

respectively). This means that within groups, pa-

tients with lower T-levels tend to have better out-

comes. However, this does not hold between groups,

(Reference Note). Because of the definition of the

dynamic range as a subtraction of the M-levels and

T-levels, the dynamic range is basally smaller in the

NPs-group as a result of the basal increase of the

T-levels (Fig. 6, C and D).

Fig. 6. T-levels of the positioner-group (P) and the nonpositioner-group (NP), shown per electrode contact (A) and per depth range

(B). The NP-group is split into the group of the first 9 shallowly inserted patients (NPs) and the last 11 deeper implanted patients

(NPd). Significant differences in basal increases in T-levels between the P-group and the NPs-group are marked (*

0.05; **

0.01). C and D show the dynamic range of each group per electrode contact (C) and per insertion range (D). The number of

patients in the ubgroups is sh wn for electrode p irs and for the depth ranges in Table 3.